Conventionally, radiography used for medical diagnostic imaging is classified into plain radiography for obtaining a still image, such as X-ray radiographing, and fluoroscopic radiography for obtaining a moving image. For each kind of radiography, there is a corresponding type of radiographing apparatus.
In recent years, a flat-panel detector has been noticed, which includes a sensor panel on which pixels, each including a conversion element to convert radiation or light from a scintillator layer into electric charges and a switch element, are arranged in a matrix on a substrate. The term “flat-panel detector” will be abbreviated to “FPD” in the following.
In particular, a conversion element prepared by using a non-crystalline semiconductor, such as amorphous silicon, and a thin film transistor prepared by using a non-crystalline semiconductor are used as described in WO 91/03745 (Published Japanese Translation of PCT Application No. H07-502865), U.S. Pat. No. 6,075,256 (Japanese Patent Application Laid-Open No. H08-116044), and U.S. Patent Application Publication 2003/0226974 (Japanese Patent Application Laid-Open 2004-015002).
For brevity, non-crystalline semiconductors will be referred to as “a-S1” in the following, and “thin film transistor” will be abbreviated to TFT in the following.
The FPD has begun to be applied to a wide range of radiography from plain radiography to fluoroscopic radiography.
Moreover, this kind of apparatus is required to decrease the dosage received by the patient, and the improvement of a signal output by the improvement of an aperture ratio and the decrease of noise are generally always required. In particular, the decrease of line noise brings about a large effect of improving the sensitivity of the FPD.
Methods of removing line noise generation factors (extrinsic factors and intrinsic factors) and methods of compensating have been considered, and various methods have been proposed as ways to compensate for noise. For example, U.S. Patent Application Publication 2006/0065845 (Japanese Patent Application Laid-Open No. 2006-101394) proposed the method of subtracting noise caused by parasitic capacitance generated at the crossing portions of signal lines and gate lines from signal outputs by arranging noise compensation lines in parallel with the signal lines. In that document, noise was considered as offset components.
Moreover, the image data of this kind of radiation detecting apparatus is obtained by taking in a dark output before radiation irradiation and a photo output after the radiation irradiation, and by deducting the dark output from the photo output.
In other words, it is always needed to deduct the dark output from the photo output in order to obtain one image, and the deduction becomes a large problem for high speed operation, that is, the improvement of operation speed in moving image driving.
At this time, although it is also considered to suppress the reading frequency of the dark output to the minimum, that is, to perform the deduction by using initial dark output data, it can be said that it is desirable to perform the deduction every time, or to perform the deduction at a certain frequency, in view of image quality.
As an example, U.S. Pat. No. 6,696,687 (Japanese Patent Application Laid-Open No. 2001-56382) also proposed to provide a dummy pixel having no photoelectric conversion element at an end of an FPD, and to remove the output of the dummy pixel from an image reading output as an offset output.